A significant amount of data, including sero-epidemiological and direct detection studies, have suggested a potential role for chronic Chlamydia pneumoniae infection in human atherosclerosis; however, a direct causal role remains to be established. Elucidation of potential pathogenic mechanisms is critical to establishing whether C. pneumoniae is merely an "innocent bystander" in atherosclerosis or possesses biological features consistent with a significant role in the initiation or exacerbation of this disease. The complete genome of C. pneumoniae has been recently sequenced and this information is important for the comprehensive investigation of proteins which C. pneumoniae can produce under various growth conditions, a process known as proteome analysis. Proteome analysis can be important for elucidation of potential functions of expressed proteins, since changes in the bacterial proteome depend on growth stages, disease states or environmental conditions. Atherosclerosis is a chronic inflammatory disease featuring an increased accumulation of smooth muscle cells, macrophages, foam cells, T-cells and lipids within the arterial intima in response to injury. Evidence exits that localizes C. pneumoniae within foam cells of human atheromas. In order for C. pneumoniae to play a causative role in atherogenesis, it would need to persist within intimal tissue for extended periods of time, thereby stimulating a chronic inflammatory response. An alteration of the normal growth cycle of C. pneumoniae can be induced, in vitro, by cytokine pretreatment of the host cell, leading to the induction of a "persistent" form of the organism. Persistence of C. pneumoniae in cells of the developing atheroma. a microenvironment containing a multitude of host cytokines, could induce a differential expression of specific bacterial proteins. Such proteins could serve as virulence factors or immunogens of C. pneumoniae, or as targets for therapeutic intervention or vaccine candidates. Investigation of C. pneumoniae protein expression in persistently infected cells by proteomic analysis will identify bacterial proteins with potential functions in atherogenesis, thus strengthening the case for a causal role of this organism in atherosclerosis. Hypothesis: Growth of C. pneumoniae in the presence of cytokines induces an altered (persistent) form that correlates with a shift in the bacterial proteome. This hypothesis will be tested by (1) determining, by proteomic analysis, alteration in protein expression patterns of C. pneumoniae when is induced into an altered (persistent) growth cycle by cytokine treatment; (2) determining the role of IDO activation in the IFN-g-mediated shift in protein expression patterns of C. pneumoniae when induced into an altered (persistent) growth cycle; and (3) determining role of additional cytokines in the shift in protein expression of C. pneumoniae when induced into an altered (persistent) growth cycle.